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Physical Changes • Physical changes only involve changes in state or appearance.• What are some examples of physical change?
Catch words for Physical Change• Boil •Split• Freeze •Grind• Melt •Cut• Condense •Crush• Break •Bend
Chemical Changes• Chemical changes and chemical properties always produce new substances.
Chemical or physical change ???• Food spoiling Chemical• Nail rusting Chemical• Oil burning Chemical• Sugar dissolving Physical• Water boiling Physical• Firefly flashing Chemical• Egg cooking Chemical• Snowflake melting Physical
Percent massPercent mass (%) = mass of element_ x 100 mass of compound
Calculations1. A 78.0 g sample of an unknown compound contains 12.4 g of hydrogen. What is the percent by mass of hydrogen in the compound?2. If 1.0 g of hydrogen reacts completely with 19.0 g of fluorine, what is the percent by mass of hydrogen in the compound that is formed?
Pure Substances• Elements are the building blocks of matter.• Atoms are the smallest part of an element.
Mixtures… do not have a definite composition… are either heterogeneous,with clearly visible components… or homogeneous, which are uniform in appearance
Solutions• Solutions are homogeneous mixtures containing a solute which is dissolved in a solvent.
Light and Energy• Frequency = f or f with units of Hertz (Hz)• Wavelength = λ with units of meters (m)
What is the relationshipbetween frequency and wavelength?
For electromagneticenergy, the equation is: c = fλ c is the speed of light c = 3.00 x 10 m/sec 8
Electromagnetic Spectrum• Electromagnetic waves carry energy. • Light is part of theelectromagnetic spectrum
The Electromagnetic Spectrumgamma rays microwaves visible light ultraviolet infraredX-rays radar radio TV Shorter wavelength Longer wavelength Higher frequency Lower frequency Higher energy Lower energy
gamma rays X-rays 400 nm ultraviolet visible light infrared microwavesIncreasing energy radar TV 700 nm radio The Electromagnetic Spectrum
The visible spectrum wasdiscovered by … Dr. Roy G. BivRed Orange Yellow Green Blue Indigo Violet 700 nm 400 nm Lower energy Higher energy
Niels BohrBohr said that electrons could exist only in certain discrete energy levels … … and that electrons can only change energy levels when they absorb or give off a certain amount of energy. (1913)
Hydrogen atomDiscrete energy levels for electronselectron nucleus
Hydrogen atomElectrons can exist in this orbit,
“Regardless of it’s shortcomings and themodifications that were laterapplied, Bohr’s model of the atom was the firstsuccessful attempt to makethe internal structure of the atom agree with spectroscopic data.” Asimov, 1964
QuantumMechanical Model of the Atom1. A small, dense positively charged nucleus which contains protons and neutrons.2. Electrons which exist outside of the nucleus at … – various distances from the nucleus, and at … – various energy levels.
The Electrons3. The electrons can have both a mass, as does matter, and a wavelength, as does light energy.4. The electrons themselves are not little solid spheres in orbit around the nucleus, but exist as a “fog” of half- energy, half-matter. The electrons can behave as either matter or energy, depending on the experiment.
Energy Levels5. Based on the ideas of Bohr, the electrons are located … – … in major energy levels, – … in energy sublevels within major energy levels, – … in orbitals within each sublevel.